Purpose: Human and macaque have similar topographic organization for V1–V3. The homology of later maps remains less clear. Macaque V4, like V2 and V3, is split into dorsal and ventral subfields. In human, one continuous hemifield map anterior to ventral V3 (V3v) was proposed as a possible homologue to macaque V4 (Brewer et al., 2005). Anterior to V3d, Larson and Heeger (2006) identified two hemifield maps (LO1/2). Hansen et al. (2007) dispute this topography, arguing that human V4, like macaque, is split into two subregions bordering V3v and V3d. We used new, model-based methods (Dumoulin & Wandell, 2007) to characterize human visual maps, population receptive field size and visual field coverage anterior to V3.

Methods: Functional magnetic resonance images were acquired while subjects viewed drifting checkerboards through a slowing moving bar aperture (field of view: 3° or 14° radius; separate experiments). A 2D Gaussian population receptive field (pRF) was fit to each voxel that best predicted the time-series. Results: All subjects showed an orderly map anterior to V3v. The map was bounded by a lower field polar angle reversal (bordering V3v) and an upper field reversal (anterior/lateral edge). The map extended ventrally to the VO maps (Brewer et al, 2005). pRF-size increased systematically with eccentricity, from &sigma; = 0.9° to 1.8°, 0.25 - 2.75° eccentricity (3° stimuli). Visual field coverage, estimated by the overlap of pRFs, varied between subjects and hemispheres, from a little over a quarterfield to a full hemifield.

Discussion: The field map adjacent to V3v appears to represent all of the contralateral hemifield in some hemispheres, but is incomplete in other cases. Further analyses will consider instrumental and biological contributions to variability, and will examine maps anterior to V3d. By estimating pRF size and visual field coverage, any possible gap in the map coverage can be quantitatively constrained.